Optical disc reproducing apparatus and operation method thereof

ABSTRACT

An optical disc reproducing apparatus includes: a decode processing circuit configured to generate decoded data by decoding encoded data read out from an optical disc such that the decoded data is written into a buffer memory, and to output a write signal to indicate a data rate when the decoded data is written in the buffer memory. A data processing circuit converts the decoded data read out from the buffer memory into an output data, and outputs a read signal to indicate a data rate when the decoded data is read out from the buffer memory. An optical disc rotation control circuit controls a number of rotations of the optical disc based on the write signal and the read signal.

INCORPORATION BY REFERENCE

This application claims priority on convention based on Japanese PatentApplication No. 2007-261152. The disclosure thereof is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disc reproducing apparatus.

2. Description of Related Art

A technique for converting analog audio data into digital audio data(hereinafter to be simply referred to as “audio data”) has been widelyknown. Compression techniques which can reduce an amount of audio dataare also known. A plurality of standards for generating compressed audiodata are known. For example, typical standards include MP3, WMA and AAC.

Along with a progress of information technology, techniques forrecording the compressed audio data on an optical information recordingmedium such as CD-R and DVD-R are widespread. The compressed audio datarecorded on the optical information recording medium is converted intoanalog audio data by an optical disc reproducing apparatus (for example,a CD drive) and then the audio data is outputted from an output unitsuch as a speaker.

The optical disc reproducing apparatus for the compressed audio data isprovided with a buffer memory. The optical disc reproducing apparatusexecutes processes such as a decoding process on read data read out fromthe optical information recording medium and held in the buffer memory,and then suppresses such fault that audio data which is being reproducedis suspended.

When data is sequentially transferred from the optical disc reproducingapparatus to a host computer, the data after a decoding operation by adecoding circuit is stored in a buffer if a transfer rate is smallerthan a read rate from the optical disc. When the read data is fullywritten into the buffer memory, a read operation from the optical discmust be brought to a halt until the buffer memory has a room forstorage. In the meantime, power may be consumed due to rotation of theoptical disc. Thus, a technique of varying rotation speed of the opticaldisc depending on an amount of data held in the buffer memory is knownin Japanese Patent Application Publication (JP-P2003-242708A:conventional example 1).

FIG. 1 is a block diagram showing an information recording discreproducing apparatus described in the conventional example 1. In theinformation recording disc reproducing apparatus described inconventional example 1, rotation of the information recording disc 103is controlled by a DVD-ROM drive 102 and a signal read from theinformation recording disc 103 is decoded by the DVD-ROM drive 102 andtransferred to a host computer 101. The DVD-ROM drive 102 includes amicroprocessor 104, a ROM 105, a buffer 106, a reproduction speedcontrol section 107, an information recording disc reading apparatus108, a decoder 109 and a RAM 110.

According to a program previously stored in the ROM 105 and aninstruction issued from the host computer 101, the microprocessor 104controls other blocks in the DVD-ROM drive 102. Data read out from theinformation recording disc 103 by the information recording disc readingapparatus 108 is supplied to a decoder 109 and decoded by the decoder109. The decoded data is sequentially stored in the buffer 106 and,after temporary storage, is transferred to the host computer 101.Depending on a transfer type such as transfer method or transfer modefor a transfer section adapted to transfer data to the host computer101, a line speed at a reproduction position of the informationrecording disc 103 is controlled to be highest line speed determinedbased on a transfer rate of each transfer type or less. By controllingthe line speed at the reproduction position of the information recordingdisc 103 so that a data transfer rate to the host computer 101 does notexceed a data rate at which the decoded data is stored in the buffer106, a high-speed rotation of the information recording disc 103 issuppressed. When the amount of data stored in the buffer 106 is apredetermined value or more, the buffer 106 is prevented from beingfully filled by reducing a rotation speed of the information recordingdisc 103.

The conventional example 1 describes a technique of an informationrecording disc reproducing apparatus which varies the rotation speed ofthe information recording disc 103 depending on a transfer section. Thedecoder 109 of the information recording disc reproducing apparatusperforms a CD decoding process and a CD-ROM decoding process to theCD-ROM disc. Here, when the data recorded on the information recordingdisc 103 is compressed audio data, the decoder 109 decodes thecompressed audio data in addition to the CD decoding process and theCD-ROM decoding process.

When multiple compressed audio data having different datacompressibilities are recorded on the information recording disc 103, adecoding process corresponding to the data compressibility is performed.For this reason, the data rate at which the decoded data is stored inthe buffer 106 varies depending on the decoding process. That is to say,when the technique described in conventional example 1 is applied to theoptical disc reproducing apparatus capable of reproducing the compressedaudio data, it may be difficult to determine a data rate in the decodingprocess. In addition, it may be difficult to determine a line speed inread of the optical disc.

Furthermore, there is a variable bit rate method in which the datacompressibility of a part of the compressed audio data is not fixed butvariable. When the technique described in conventional example 1 isapplied to the optical disc reproducing apparatus capable of reproducingthe compressed audio data, it is difficult to cope with variance of adecoded data rate.

Unlike an apparatus in which the line speed of the optical disc can becalculated by an external transfer section, the line speed of theoptical disc which stores the compressed audio data cannot be previouslyknown. Thus, conventional systems cannot rotate at a low speed andcontrol the optical disc which stores the compressed audio data. Thereis a conventional method of monitoring the number of stages of FIFO andperforming a phase comparison of data write/read into/from a buffermemory. However, when data rates of data write/read into/from the buffermemory are different or the data rate is extremely low, there is notechnique for coping with such a state.

SUMMARY

In an aspect of the present invention, an optical disc reproducingapparatus includes: a decode processing circuit configured to generatedecoded data by decoding encoded data read out from an optical disc suchthat the decoded data is written into a buffer memory, and to output awrite signal to indicate a data rate when the decoded data is written inthe buffer memory; a data processing circuit configured to convert thedecoded data read out from the buffer memory into an output data, and tooutput a read signal to indicate a data rate when the decoded data isread out from the buffer memory; and an optical disc rotation controlcircuit configured to control a number of rotations of the optical discbased on the write signal and the read signal.

In another aspect of the present invention, an operation method of anoptical disc reproducing apparatus, includes: generating decoded data bydecoding encoded data read out from an optical disc such that thedecoded data is written into a buffer memory; generating a write signalto indicate a data rate when the decoded data is written in the buffermemory; converting the decoded data read out from the buffer memory intoan output data; generating a read signal to indicate a data rate whenthe decoded data is read out from the buffer memory; and controlling anumber of rotations of the optical disc based on the write signal andthe read signal.

In another aspect of the present invention, an operation method of anoptical disc reproducing apparatus, which includes: a decode processingcircuit configured to generate decoded data by decoding encoded dataread out from an optical disc to supply the decoded data into a buffermemory; a data processing circuit configured to convert the decoded dataread out from the buffer memory into an output data; and an optical discrotation control circuit configured to control a number of rotations ofthe optical disc, the operation method includes: the decode processingcircuit generating a write signal to indicate a data rate when thewrites the decoded data is written in the buffer memory; the dataprocessing circuit generating a read signal to indicate a data rate whenthe decoded data is read out from the buffer memory; and the opticaldisc rotation control circuit controlling a number of rotations of theoptical disc based on the write signal and the read signal.

When the compressed decoded data is outputted, the data rate at whichthe compressed data is read from the buffer memory is low. In thepresent invention, the rotation of the optical disc is made low due tothe low data rate so that the buffer memory is not be fully filled.

When data obtained by decompressing the compressed audio data isoutputted, the data rate at which data is outputted from the buffermemory lowers according to the data compressibility of the compressedaudio data. In the present invention, the disc is rotated at a low speedso that a data input rate to the buffer memory is made lower incorrespondence to a lower data output rate from the buffer memory. Forexample, in case of the disc in which the compressed audio data incompressibility of 1/10 has been recorded, the rotation speed can bemade 1/10 of normal reproduction.

By varying the rotation speed of the disc continuously (in a smallupdate interval) in a small step (a small change), an out-of-lock in thePLL circuit for generating a bit clock signal from an EFM signal can beprevented and an error rate during a variation in rotation of the disccan be reduced.

Further, in the reproduction of the compressed audio data, a frequencyof access to the buffer memory is decreased. In addition, a timeinterval of monitoring and update of the disc rotation control isreduced.

Furthermore, by preventing overflow/underflow, re-access to the disc isreduced, thereby reducing loads imposed on the CPU. In addition, sincethe disc rotation control is not performed by the microprocessor, loadsimposed on the microprocessor can be advantageously reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description ofcertain embodiments taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a block diagram showing a configuration of a conventionalinformation recording disc reproducing apparatus;

FIG. 2 is a block diagram showing a configuration of an optical discreproducing apparatus according to a first embodiment of the presentinvention;

FIG. 3 is a block diagram showing a configuration of an optical discrotation control data generating circuit in the first embodiment;

FIG. 4 shows timing charts in an operation of the optical disc rotationcontrol data generating circuit in the first embodiment;

FIG. 5 is a block diagram showing a configuration of the optical discrotation control data generating circuit of the optical disc reproducingapparatus according to a second embodiment of the present invention;

FIG. 6 is a table showing a correspondence of a coefficient P and acondition; and

FIG. 7 is a view showing a relation of optical disc rotation controldata and an UP-DOWN count value in the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an optical disc reproducing apparatus of the presentinvention will be described in detail with reference to the attacheddrawings. In the following description, a case will be described that atransfer method is PIO transfer or multi-word DMA transfer. Also, thedescription will be carried out in accordance with a case that atransfer mode indicates a transfer rate determined for each transfermethod. Thus, for example, in case of the multi-word DMA transfer,

in a mode 0, the transfer rate is about 4.16 [MB/s],

in a mode 1, the transfer rate is about 13.33 [MB/s], and

in a mode 2, the transfer rate is about 16.67 [MB/s].

First Embodiment

FIG. 2 is a block diagram showing a configuration of an optical discreproducing apparatus 20 according to a first embodiment of the presentinvention. An optical disc 1 is mounted on or taken out from the opticaldisc reproducing apparatus 20. The optical disc 1 is, for example, aCD-ROM, a DVD-ROM, a rewritable CD-R/RW or DVD-R/RW or the like.

The optical disc reproducing apparatus 20 includes a spindle motor 2, anoptical pickup 3, an RF amplifier 4, a servo signal processing circuit5, a digital decoding circuit 6, an optical disc rotation control datagenerating circuit 7, a buffer memory 8, a memory controller 9, an errorcorrection circuit 10 and a compressed audio data reproducing circuit11.

The spindle motor 2 rotates the optical disc 1. The spindle motor 2changes the rotation speed of the optical disc 1 in response to aspindle control signal. The optical pickup 3 includes a semiconductorlaser (not shown) and a photodetector (not shown). The optical pickup 3reads data recorded on the optical disc 1 and outputs the data in theform of an electrical signal. The RF amplifier 4 amplifies theelectrical signal outputted from the optical pickup 3 and outputs an EFM(eight to fourteen modulation) signal to the digital decoding circuit 6.The digital decoding circuit 6 decodes the EFM signal outputted from theRF amplifier 4 into a digital data and outputs as a write decoded data21 to the memory controller 9. The digital decoding circuit 6 outputs awrite signal 24 to the memory controller 9 and the optical disc rotationcontrol data generating circuit 7. The write signal 24 is a signal forallowing the memory controller 9 to store the write decoded data 21 inthe buffer memory 8.

The memory controller 9 controls an access to the buffer memory 8. Thememory controller 9 stores the write decoded data 21 as write data inthe buffer memory 8 in response to the write signal 24 outputted fromthe digital decoding circuit 6. The memory controller 9 reads the storeddata as read data from the buffer memory 8 in response to a read signal23 outputted from the compressed audio data reproducing circuit 11 andsupplies the read data as read decoded data 22 to the compressed audiodata reproducing circuit 11.

The error correction circuit 10 performs a CRC error check to the writedecoded data 21 supplied to the memory controller 9. When an error isfound in the write decoded data 21, the error correction circuit 10corrects the error of the write decoded data 21. The memory controller 9may read the data stored in the buffer memory 8 in response to a requestof the error correction circuit 10.

The compressed audio data reproducing circuit 11 outputs the read signal23 to the memory controller 9 and receives the read decoded data 22 asread data from the buffer memory 8. The compressed audio datareproducing circuit 11 decodes the compressed audio data and outputs thedecoded data as audio data. It should be noted that in the presentembodiment, the optical disc rotation control data generating circuit 7generates optical disc rotation control data 25 in response to the readsignal 23 and the write signal 24. The control data generating circuit 7outputs the optical disc rotation control data 25 to the servo signalprocessing circuit 5. The servo signal processing circuit 5 outputs aspindle control signal to the spindle motor 2 in response to the opticaldisc rotation control data 25. The spindle motor 2 controls a rotationspeed of the optical disc 1 in response to the spindle control signal.

FIG. 3 is a block diagram showing a configuration of the optical discrotation control data generating circuit 7. The control data generatingcircuit 7 includes a first counter 12, a second counter 13, a phasedifference data calculating circuit 14, an UP-DOWN counter 15, a firstcycle difference data calculating circuit 16 and an adding circuit 17.The write signal 24 is supplied from the above-mentioned digitaldecoding circuit 6 to the control data generating circuit 7 and to thememory controller 9. The read signal 23 is supplied from the compressedaudio data reproducing circuit 11 to the control data generating circuit7 and the memory controller 9.

The first counter 12 counts the read signal 23 from 0 to a first countermaximum value (N−1) (N is a constant inherent in system), and outputs afirst counter value n as the count value. An operation in which thefirst counter 12 counts from 0 to the first counter maximum value (N−1)is supposed to be one cycle. The first counter 12 returns the firstcounter value n to 0 after to the first counter maximum value (N−1), andcontinues the counting operation in a new cycle. The first counter 12generates a first counter cycle signal in the form of pulse attransition from the first counter maximum value (N−1) to 0.

The second counter 13 counts the write signal 24 from 0 to a secondcounter maximum value (M−1) (M is a constant inherent in system) and thecount value is a second counter value m. The second counter 13 returnsthe second counter value m to 0 after the second counter maximum value(M−1), and continues the counting operation in a new cycle. The secondcounter 13 generates a second counter cycle signal in the form of pulseat transition from the second counter maximum value (M−1) to 0.

The first counter value n of the first counter 12 and the second countervalue m of the second counter 13 are supplied to the phase differencedata calculating circuit 14. The phase difference data calculatingcircuit 14 performs a following calculation:Phase difference data 72=(M−1)×n−(N−1)×mThe calculating circuit 14 outputs the phase difference data 72.

The first counter cycle signal of the first counter 12 and the secondcounter cycle signal of the second counter 13 are supplied to theUP-DOWN counter 15. The UP-DOWN counter 15 is incremented in response tothe first counter cycle signal from the first counter 12 and decrementedin response to the second counter cycle signal from the second counter13. The count value of the UP-DOWN counter 15 is supplied to the firstcycle difference data calculating circuit 16. The difference datacalculating circuit 16 performs the following calculation:Cycle difference data 73=(UP-DOWN counter value 71)×(second countermaximum value (M−1))×(first counter maximum value (N−1))The difference data calculating circuit 16 outputs the cycle differencedata 73 to the adding circuit 17. Based on the phase difference data 72and the cycle difference data 73, the adding circuit 17 performs thefollowing calculation:Optical disc rotation control data 25=(phase difference data 72)+(cycledifference data 73)The adding circuit 17 outputs the optical disc rotation control data 25.

When the write decoded data 21 is CD-ROM data and a SYNC pattern of aCD-ROM format is detected and the data amount of 98×24=2352 bytes isrecognized as a one sector length of the CD-ROM data, when the data 21is stored in the buffer memory 8 via the memory controller 9. 2368bytes, which is a sum of 2340 bytes obtained by subtracting 12 bytes ofthe sync pattern from the sector data and subcode data subjected to aCIRC decoding process in addition to digital decoding process of discdata in the digital decoding circuit 6, is stored in the buffer memory 8as data of one sector.

The compressed audio data stored in the buffer memory 8 as CD-ROM datais read from the buffer memory 8 via the memory controller 9 as the readdecoded data 22 in response to the read signal 23 from the compressedaudio data reproducing circuit 11. However, a parity portion used forerror correction in the CD-ROM error correction circuit 10 isunnecessary, and 2048 bytes per sector are read by the compressed audiodata reproducing circuit 11 as the read decoded data 22. That is, fordata which is written into the buffer memory 8 as the write decoded data21 and read from the buffer memory 8 as the read decoded data 22 in anactual system,

the number of write data per sector is 2368 bytes, and

the number of read data per sector is 2048 bytes.

Given that a common divisor L exists,2368(940H)=L×M and2048(800H)=L×N,L=64(40H), and M=37(25H), N=32(20H) are obtained.

The optical disc rotation control data generating circuit 7 normalizesthe first counter value n of the first counter 12 and the second countervalue m of the second counter 13 based on the maximum values N−1 andM−1, respectively, such that the maximum values are “1”. The controldata generating circuit 7 controls rotation of the optical disc 1 sothat the first counter value n/first counter maximum value (N−1) may beequal to the second counter value m/second counter maximum value (M−1)in phase and period.

The phase difference can be obtained from the following calculation:phase difference=first counter value n/first counter maximum value(N−1)−the second counter value m/second counter maximum value (M−1)(Maximum value: 1)

Meanwhile, a cycle difference can be obtained as a value of the UP-DOWNcounter 15 which is incremented by 1 in case of one cycle of the firstcounter value n of the first counter 12 and is decremented by 1 in caseof one cycle of the second counter value m of the second counter 13.Rotation of the disc is controlled so that a sum of the phase differenceand the cycle difference may become 0.

In an actual circuit, from the following calculations:phase difference data 72=second counter maximum value (M−1)×n−firstcounter maximum value (N−1)×m,maximum value=second counter maximum value (M−1)×first counter maximumvalue (N−1), andminimum value: −1×second counter maximum value (M−1)×first countermaximum value (N−1),the phase difference data calculating circuit 14 performs the abovephase difference operation to output the phase difference data 72. Here,Constant S=second counter maximum value (M−1)×first counter maximumvalue (N−1),the maximum value of the phase difference data 72 is 1×S and the minimumvalue of the phase difference data 72 is −1×S. The UP-DOWN count value71 of the UP-DOWN counter 15 is multiplied by second counter maximumvalue (M−1)×first counter maximum value (N−1)=S to obtain the cycledifference data 73. The first cycle difference data calculating circuit16 performs this cycle difference data operation:

$\begin{matrix}{{{Cycle}\mspace{14mu}{difference}\mspace{14mu}{data}\mspace{14mu} 73} = {{UP}\text{-}{DOWN}\mspace{14mu}{count}\mspace{14mu}{value}\mspace{14mu} 71 \times}} \\{{second}\mspace{14mu}{counter}\mspace{14mu}{maximum}\mspace{14mu}{value}} \\{( {M\text{-}1} ) \times {first}\mspace{14mu}{counter}\mspace{14mu}{maximum}} \\{{value}\mspace{14mu}( {N\text{-}1} )} \\{= {{UP}\text{-}{DOWN}\mspace{14mu}{count}\mspace{14mu}{value}\mspace{14mu} 71 \times S}}\end{matrix}$to output the cycle difference data 73. The phase difference data 72 asan output of the phase difference data calculating circuit 14 is addedto the cycle difference data 73 as an output of the first cycledifference data calculating circuit 16 by the adding circuit 17 to findthe optical disc rotation control data 25.Optical disc rotation control data 25=phase difference data 72+cycledifference data 73

Rotation of the optical disc 1 is controlled so that the optical discrotation control data 25 may be 0, that is, a sum of phase differenceand cycle difference of write/read data into/from the buffer memory 8.Calculation of the phase difference data 72, the cycle difference data73 and the optical disc rotation control data 25 may be performed at anyfixed cycle. Generally, it is desired that the cycle is the same as anupdate cycle of the spindle control signal in servo signal processing.

FIG. 4 is timing charts showing an operation of the optical discrotation control data generating circuit 7. A horizontal axis in FIG. 4represents time course. A portion (a) of FIG. 4 shows time variation ofthe product of the first counter value n and a second counter maximumvalue (M−1) M−1 in response to the read signal 23 and a product of thesecond counter value m and a first counter maximum value (N−1) N−1 inresponse to the write signal 24. The portion (a) of FIG. 4 shows a casethat the first counter value n in response to the read signal 23 and thesecond counter value m in response to the write signal 24 areincremented at different data rates.

The portion (a) of FIG. 4 shows a first operation result a1=secondcounter maximum value (M−1)×n as a dotted line and a second operationresult a2=first counter maximum value (N−1)×m as a solid line. A portion(b) of FIG. 4 shows a time variation of the UP-DOWN count value 71. Theportion (b) of FIG. 4 shows an output of the UP-DOWN counter 15 withrespect to the first operation result a1 and the second operation resulta2. A portion (c) of FIG. 4 shows time variation of the UP-DOWN countvalue 71. The phase difference data 72 shown in the portion (c) of FIG.4 is an output of the phase difference data calculating circuit 14 andrepresents the difference between the first operation result a1 and thesecond operation result a2. A portion (d) of FIG. 4 shows time variationof the cycle difference data 73. The portion (d) of FIG. 4 also showstime variation of the optical disc rotation control data 25. The cycledifference data 73 shown in the portion (d) of FIG. 4 is an output ofthe first cycle difference data calculating circuit 16 with respect tothe UP-DOWN count value 71 shown in the portion (b) of FIG. 4. Theoptical disc rotation control data 25 shown in the portion (d) of FIG. 4is an output of the adding circuit 17 which is obtained by adding thephase difference data 72 to the cycle difference data 73 in the portion(c) of FIG. 4. A time axis thereof is common in the above-mentionedportions (a) to (d) of FIG. 4.

In the portion (a) of FIG. 4, inclinations of the first operation resulta1 and the second operation result a2 represent data rates of the readsignal and the write signal, respectively. Although the data rate of thefirst operation result a1 is initially greater than that of the secondoperation result a2, the data rate of the first operation result a1becomes smaller than that of the second operation result a2 on the way.

In case of the first operation result a1>the second operation result a2in the data rate, since the phase difference data 72 is the firstoperation result a1−the second operation result a2, it has an increasingpositive inclination. When the frequency of the first counter cyclesignal of the first counter 12 is higher than that of the second countercycle signal of the second counter 13, the UP-DOWN count value 71 in theportion (b) of FIG. 4 is incremented.

In case of the first operation result a1<the second operation result a2in the data rate, since the phase difference data 72 is the firstoperation result a1−second operation result a2, it has a decreasingnegative inclination. When the frequency of the second counter cyclesignal of the second counter 13 is higher than that of the first countercycle signal of the first counter 12, the UP-DOWN count value 71 in theportion (b) of FIG. 4 is decremented.

In case of the first operation result a1>the second operation result a2in the data rate, the optical disc rotation control data 25 has anincreasing positive inclination, and in case of the first operationresult a1<the second operation result a2 in the data rate, the opticaldisc rotation control data 25 has a decreasing negative inclination.

It is considered that, when the state of the first operation resulta1>the second operation result a2 in data rate continues, the opticaldisc rotation control data 25 in the portion (d) of FIG. 4 moves towarda positive value, and when the state of the first operation resulta1<the second operation result a2 continues, the optical disc rotationcontrol data 25 in the portion (d) of FIG. 4 moves toward a negativevalue. That is, as the data rate of the read signal is increased, apositive value of the optical disc rotation control data 25 becomesgreater, and as the data rate of the write signal is increased, anegative value of the optical disc rotation control data 25 becomesgreater.

It is assumed that, when the value of the spindle control signaloutputted from the servo signal processing circuit 5 to the spindlemotor 2 is 0, the spindle motor 2 is in a stopped state and then, as thevalue of the spindle control signal is greater, the spindle motor 2rotates at a higher speed.

It is assumed that, when the value of the optical disc rotation controldata 25 as the output of the optical disc rotation control datagenerating circuit 7 is 0, the spindle control signal outputted from theservo signal processing circuit 5 to the spindle motor 2 has an offsetvalue for rotating the optical disc 1 at a fixed speed. In the servosignal processing circuit 5, the value of the optical disc rotationcontrol data 25 is added to the offset value to output the spindlecontrol signal.

When the data rate of the read signal is greater than that of the writesignal, a positive value is outputted as the optical disc rotationcontrol data 25, and accordingly, the servo signal processing circuit 5receives the positive value and outputs a spindle control signal toallow the spindle motor 2 to rotate at a higher speed. Contrarily, whenthe data rate of the write signal is greater than that of the readsignal, a negative value is outputted as the optical disc rotationcontrol data 25, and accordingly, the servo signal processing circuit 5receives the negative value and outputs a spindle control signal belowthe offset value, to allow the spindle motor 2 to rotate at a lowerspeed.

When the data rate of the read signal 23 is greater than that of thewrite signal 24, the frequency at which the decoded data stored in thebuffer memory 8 is read out as the read decoded data 22 is high, and thedecoded data stored in the buffer memory 8 continues to decrease. In thepresent embodiment, when the data rate of the read signal 23 is greaterthan that of the write signal 24, the following relation in the datarate: the first operation result a1>the second operation result a2 inFIG. 4 is established. Thus, the optical disc rotation control data 25of the optical disc rotation control data generating circuit 7 movestoward a positive value, and accordingly, the servo signal processingcircuit 5 receives the positive value and outputs the spindle controlsignal to allow the spindle motor 2 to rotate at a higher speed. Thus,the rotation speed of the optical disc 1 is increased to increase thewrite data 21 as write decoded data 21 and the data rate of the writesignal 24. That is, when the data rate of the write signal 24 is smallerthan that of the read signal 23, the rotation speed of the optical disc1 is increased, thereby preventing decoded data stored in the buffermemory 8 from continuously decreasing. Similarly, when the data rate ofthe write signal 24 is larger than that of the read signal 23, thefrequency at which the decoded data stored in the buffer memory 8 iswritten as the write decoded data 21 is high, and thus, the decoded datastored in the buffer memory 8 continues to increase.

In the present embodiment, when the data rate of the write signal 24 islarger than that of the read signal 23, the following relation in datarate: first operation result a1<second operation result a2 is satisfiedin FIG. 4. Consequently, the optical disc rotation control data 25 ofthe optical disc rotation control data generating circuit 7, movestoward a negative value, and accordingly, the servo signal processingcircuit 5 receives the negative value and outputs the spindle controlsignal to allow the spindle motor 2 to rotate at a lower speed. Thereby,the rotation speed of the optical disc 1 is decreased to decrease writedata as the write decoded data 21 and the data rate of the write signal24. That is, when the data rate of the write signal 24 is larger thanthat of the read signal 23, the rotation speed of the optical disc 1 isdecreased, thereby preventing the decoded data stored in the buffermemory 8 from continuously increasing.

To enhance understanding of the operation in the present embodiment, inFIG. 4, the phase difference data 72, the cycle difference data 73 andthe optical disc rotation control data 25 are shown as continuouswaveform. These waveforms do not limit an operation of the optical discreproducing apparatus 20 in the present embodiment. It is preferred toperform calculation at the update timing of the optical disc rotationcontrol data 25.

Second Embodiment

Hereinafter, the optical disc reproducing apparatus according to asecond embodiment of the present invention will be described. FIG. 5 isa block diagram showing a configuration of the optical disc rotationcontrol data generating circuit 7 in the second embodiment of thepresent invention. The control data generating circuit 7 in the secondembodiment generates the optical disc rotation control data 25 withoutperforming the phase difference data calculation. Referring to FIG. 5,the control data generating circuit 7 in the second embodiment includesthe first counter 12, the second counter 13, the UP-DOWN counter 15 anda second cycle difference data calculating circuit 18.

As in the first embodiment, the read signal 23 is outputted from thecompressed audio data reproducing circuit 11 to the memory controller 9.The memory controller 9 outputs data stored in the buffer memory 8 asthe read decoded data 22 in response to the read signal 23, and suppliesthe data to the compressed audio data reproducing circuit 11.

As in the first embodiment, the write signal 24 is outputted from thedigital decoding circuit 6 to the memory controller 9. The memorycontroller 9 stores the write decoded data 21 outputted from the digitaldecoding circuit 6 in the buffer memory 8 in response to the writesignal 24. The first counter 12, the second counter 13 and the UP-DOWNcounter 15 have a same configuration and operation as those in the firstembodiment. As shown in FIG. 5, the first counter cycle signal as anoutput of the first counter 12 and the second counter cycle signal as anoutput of the second counter 13 are supplied to the UP-DOWN counter 15.The UP-DOWN counter value 71 as the output of the UP-DOWN counter 15 issupplied to the second cycle difference data calculating circuit 18. Thesecond cycle difference data calculating circuit 18 outputs the opticaldisc rotation control data 25 based on the UP-DOWN counter value 71. Thesecond cycle difference data calculating circuit 18 in the secondembodiment multiplies the UP-DOWN counter value 71 by a coefficient Pand generates the optical disc rotation control data 25.

FIG. 6 is a table showing a relation of the coefficient P and acondition (hereinafter to be referred to as a correspondence table 31).The correspondence table 31 includes a condition region 32 and acoefficient region 33. The coefficient P takes any of values of P1, P2and P3 depending on the UP-DOWN counter value 71 as the output of theUP-DOWN counter 15. It should be noted that the following relation ofP1<P2<P3 is maintained. Referring to FIG. 6,in case of −UD1<UP-DOWN counter value 71<UD1, the coefficient P=P1,in case of −UD2≦UP-DOWN counter value 71≦−UD1, the coefficient P=P2,in case of UD1<UP-DOWN counter value 71≦UD2, the coefficient P=P2,in case of UP-DOWN counter value 71<−UD2, the coefficient P=P3, andin case of UD2≦UP-DOWN counter value 71, the coefficient P=P3.

FIG. 7 is a graph showing a characteristic of the optical disc rotationcontrol data 25—the UP-DOWN counter value 71 in the second embodiment.In FIG. 7, a horizontal axis represents the UP-DOWN counter value 71 asthe output of the UP-DOWN counter 15, and a vertical axis represents theoptical disc rotation control data 25 as the output of the optical discrotation control data generating circuit 7.

When an absolute value of the UP-DOWN counter value 71 is large, thatis, the cycle difference between write and read of data into and fromthe buffer memory 8 is large, there is a possibility that a data amountin the buffer memory 8 varies more than a predetermined amount, leadingto overflow or underflow of the buffer. The optical disc rotationcontrol data generating circuit 7 in the second embodiment prevents theabove-mentioned possibility by taking the value of the coefficient Plarge, thereby increasing variation in the optical disc rotation controldata 25, in turn, and the amount of correction of an optical discrotation control.

When the absolute value of the UP-DOWN counter value 71 is small, thatis, a variation in the amount of data in the buffer memory 8 is small,the optical disc rotation control data generating circuit 7 in thesecond embodiment makes the coefficient P small, thereby decreasing thevariation in the optical disc rotation control data 25, in turn, theamount of correction of the optical disc rotation control. Thereby,since the variation in the rotation of the optical disc 1 is decreased,an amount of jitter of a bit clock generated in a PLL circuit is alsodecreased, reducing an error rate in the decoding process.

A gain to the variation in the amount of data stored in the buffermemory 8 is assumed to be non-uniform, and when the variation in thedata amount is large, the possibility of overflow/underflow of thebuffer is rapidly avoided by increasing the gain, and when the variationin the data amount is small, the variation in the rotation of theoptical disc 1 is decreased by decreasing the gain to lower an errorrate in the decoding process.

When an update cycle of the optical disc rotation control data 25 issufficiently larger than cycles of the first counter 12 and the secondcounter 13 and cycle difference data rather than phase difference datadominantly contributes to the optical disc rotation control data 25, itis preferred to apply the configuration in the second embodiment.Furthermore, the cycle difference data calculation based on thecoefficient P which varies depending on the value of the UP-DOWN counter15 in the second embodiment may be used also in the first embodiment.The coefficient P which varies depending on a value of the UP-DOWNcounter 15 is not limited to P1, P2 and P3.

In the above embodiments, timing when the phase difference data 72 andthe cycle difference data 73 are updated may be a time when the writesignal 24 or the read signal 23 is generated or a time when the cyclesignal of the first counter 12 or the second counter 13 is generated.

Comparative Example

When the compressibility is known for each music data in compressedaudio data, a data rate of decoded data in a CD decoding process, aCD-ROM decoding process and a compressed audio data decoding process canbe found. However, there is a variable bit rate method in which the datacompressibility of a part of compressed audio data is not fixed butvaries. Conventional examples cannot cope with the varying decoded datarate.

The conventional example will be described in which a line speed in readof an optical disc is given in advance. Data read out from aninformation recording disc 103 by an information recording disc readingapparatus 108 is influenced by a variation in the rotation of the disc.For this reason, the data cannot be fetched as it is while using a fixedclock signal. Generally, a bit clock signal which is phase-locked to thedata by a PLL circuit is generated and the data is synchronized with thebit clock signal and decoded as digital data. It is assumed that theinformation recording disc reading apparatus 108 in the conventionalexample includes the PLL circuit for generating the bit clock signalphase locked to read data.

In the conventional technique, switching of the rotation of theinformation recording disc 103 is performed between a rotation speed Rccorresponding to a transfer rate to the host computer 101 and a lowrotation speed Rc/N (for example, N=2, N is an optional fixed value)when a certain amount of data or more have been stored in the buffer 106or when an error occurs a predetermined number of times or more in thedecoding process.

In the binary switching of rotation speed, however, when a difference inspeed at the switching of rotation speed is large, the phase-lockedstate of the PLL circuit for generating the bit clock signal to the readsignal cannot be maintained and a normal clock generation cannot beachieved, so that there is a possibility that the data error rate may belarge, while the rotation speed is largely varying. Further, when a timeinterval during which a reproduction speed is monitored is long,overflow/underflow of the buffer memory may occur during the decodingprocess. Furthermore, according to the conventional example, since amicroprocessor carries out monitoring of a line speed and setting of arotation speed in a disc rotation control, it is difficult to reduceloads imposed on the microprocessor.

Although the present invention has been described above in connectionwith several embodiments thereof, it would be apparent to those skilledin the art that those embodiments are provided solely for illustratingthe present invention, and should not be relied upon to construe theappended claims in a limiting sense.

1. An optical disc reproducing apparatus comprising: a decode processingcircuit configured to generate decoded data by decoding encoded dataread out from an optical disc such that the decoded data is written intoa buffer memory, and to output a write signal to indicate a data ratewhen the decoded data is written in said buffer memory; a dataprocessing circuit configured to convert the decoded data read out fromsaid buffer memory into output data, and to output a read signal toindicate a data rate when the decoded data is read out from said buffermemory; and an optical disc rotation control circuit configured tocontrol a number of rotations of said optical disc based at least inpart on the write signal and the read signal, wherein said optical discrotation control circuit comprises: a first counter configured to outputa first counter value based on the write signal; a second counterconfigured to output a second counter value based on the read signal; aphase difference data calculating circuit configured to multiplypredetermined fixed values with the first counter value and the secondcounter value, respectively, and to calculate a difference between themultiplication results; an UP-DOWN counter configured to output a thirdcounter value based on a number of cycles of said first counter and anumber of cycles of said second counter; a cycle difference datacalculating circuit configured to calculate a difference of the numberof cycles of said first counter and the number of cycles of said secondcounter based on the third counter value; and an adding circuitconfigured to add an output of said phase difference data calculatingcircuit and an output of said cycle difference data calculating circuitfor calculation of a summation, wherein the number of rotations of saidoptical disc is controlled based at least in part on the summation. 2.The optical disc reproducing apparatus according to claim 1, whereinsaid first counter restarts a count operation from an initial countvalue when the first counter value reaches a maximum count value, andsupplies a first cycle number indicating a number of times of therestart to said UP-DOWN counter, said second counter restarts a countoperation from an initial count value when the second counter valuereaches a maximum count value, and supplies a second cycle numberindicating a number of times of the restart to said UP-DOWN counter, andsaid UP-DOWN counter generates a new third counter value by adding apredetermined value to the third counter value in response to the firstcycle number, and generates a new third counter value by subtracting apredetermined value from the third counter value in response to thesecond cycle number.
 3. An optical disc reproducing apparatuscomprising: a decode processing circuit configured to generate decodeddata by decoding encoded data read out from an optical disc such thatthe decoded data is written into a buffer memory, and to output a writesignal to indicate a data rate when the decoded data is written in saidbuffer memory; a data processing circuit configured to convert thedecoded data read out from said buffer memory into an output data, andto output a read signal to indicate a data rate when the decoded data isread out from said buffer memory; and an optical disc rotation controlcircuit configured to control a number of rotations of said optical discbased at least in part on the write signal and the read signal, whereinsaid optical disc rotation control circuit comprises: a first counterconfigured to output a number of cycles of a first counter value whichis calculated based on the write signal; a second counter configured tooutput a number of cycles of a second counter value which is calculatedbased on the read signal; and an UP-DOWN counter configured to output athird counter value based on the number of cycles of said first counterand the number of cycles of said second counter, wherein the rotation ofsaid optical disc is controlled based at least in part on a differenceof the number of cycles of said first counter and the number of cyclesof said second counter which difference is obtained based on the thirdcounter value.
 4. An operation method of an optical disc reproducingapparatus, comprising: generating decoded data by decoding encoded dataread out from an optical disc such that the decoded data is written intoa buffer memory; generating a write signal to indicate a data rate whenthe decoded data is written in said buffer memory; converting thedecoded data read out from said buffer memory into output data;generating a read signal to indicate a data rate when the decoded datais read out from said buffer memory; and controlling a number ofrotations of said optical disc based at least in part on the writesignal and the read signal, wherein said controlling comprises:generating a first counter value based on the write signal; generating asecond counter value based on the read signal; multiplying predeterminedfixed values with the first counter value and the second counter value,respectively, to calculate a phase difference between the multiplicationresults; generating a third counter value based on a number of cycles ofsaid first counter and a number of cycles of said second counter;calculating a cycle difference of the number of cycles of said firstcounter and the number of cycles of said second counter based on thethird counter value; adding the phase difference and the cycledifference for calculation of a summation; and controlling the number ofrotations of said optical disc based at least in part on the summation.5. The operation method according to claim 4, further comprising:generating a first cycle number indicating a number of times of restartwhile a count operation is restarted from an initial count value whenthe first counter value reaches a maximum count value; generating asecond cycle number indicating a number of times of restart while acount operation is restarted from an initial count value when the secondcounter value reaches a maximum count value; generating a new thirdcounter value by adding a predetermined value to the third counter valuein response to the first cycle number; and generating a new thirdcounter value by subtracting a predetermined value from the thirdcounter value in response to the second cycle number.
 6. An operationmethod of an optical disc reproducing apparatus, comprising: generatingdecoded data by decoding encoded data read out from an optical disc suchthat the decoded data is written into a buffer memory; generating awrite signal to indicate a data rate when the decoded data is written insaid buffer memory; converting the decoded data read out from saidbuffer memory into output data; generating a read signal to indicate adata rate when the decoded data is read out from said buffer memory; andcontrolling a number of rotations of said optical disc based at least inpart on the write signal and the read signal, wherein said controllingcomprises: generating a number of cycles of a first counter value whichis calculated based on the write signal; generating a number of cyclesof a second counter value which is calculated based on the read signal;generating a third counter value based on the number of cycles of saidfirst counter and the number of cycles of said second counter;controlling the rotation of said optical disc based at least in part ona difference of the number of cycles of said first counter and thenumber of cycles of said second counter which difference is obtainedbased on the third counter value.
 7. An operation method of an opticaldisc reproducing apparatus which comprises a decode processing circuitconfigured to generate decoded data by decoding encoded data read outfrom an optical disc to supply the decoded data into a buffer memory; adata processing circuit configured to convert the decoded data read outfrom said buffer memory into an output data and an optical disc rotationcontrol circuit configured to control a number of rotations of saidoptical disc, said operation method comprising: said decode processingcircuit generating a write signal to indicate a data rate when thewrites the decoded data is written in said buffer memory; said dataprocessing circuit generating a read signal to indicate a data rate whenthe decoded data is read out from said buffer memory; and said opticaldisc rotation control circuit controlling a number of rotations of saidoptical disc based on the write signal and the read signal, wherein saidcontrolling comprises: outputting the number of cycles of a firstcounter value which is calculated based on the write signal; outputtingthe number of cycles of a second counter value which is calculated basedon the read signal; outputting a third counter value based on the numberof cycles of the first counter and the number of cycles of the secondcounter.